Mosasaurs were serpentine marine reptiles and ferocious predators. Mosasaurs were not dinosaurs but evolved from semi-aquatic squamates known as the aigialosaurs, close relatives of modern-day monitor lizards and snakes. This happened about 95 MYA, during the Cenomanian age of the Cretaceous.
Mosasaurs breathed air and were powerful swimmers that were well-adapted to living in the warm, shallow epicontinental seas prevalent during the late Cretaceous period. The first representatives of this group were small reptiles, such as Dallasaurus, but eventually they evolved into such giants as Tylosaurus, a monstrous marine lizard. Mosasaurs are intensely territorial and cannibals, and the only meetings between two Mosasaurs that didn’t end in violence occur was when the Mosasaurs in question were of opposite sexes, and there was the possibility of mating.
The mosasaurs were one of the success stories of the late Cretaceous period. Giant Mosasaurs were the top predator in the Cretaceous seas and were widespread across the world. Much of their day would have been spent swimming slowly near the seabed looking for suitable prey to attack.
Their diet consisted of slow moving animals like ammonites, birds and turtles but they would also tackle larger and swifter prey, such as sharks and plesiosaurs, when the opportunity arose. As Mosasaurs were not fast swimmers they would have stalked their prey using natural cover provided by seaweed and rocks. Only when the prey was within striking range would a mosasaur propel itself forward. Being caught in a mosasaur’s jaws meant almost certain death. Although giant Mosasaurs were the top predators in the sea, they were still vulnerable to attack. One mosasaur fossil bears the marks of a shark bite in its spine.
All mosasaurs died out 65 MYA, during the K/T extinction.
Appearance in other Media
Read more at the Anomaly Research Centre
In 1X03, a giant mosasaur enters through an anomaly and begins to harass the people of London; eventually it gets back and gets eaten by a bigger, older mosasaur.